Thin-film resistor with high temperature coefficient for use as passive semiconductor component for integrated circuits, and method for producing the same

ABSTRACT

The invention relates to a semiconductor component with a WSiN layer as thin-film resistor with high temperature coefficient for use as thermistor in bolometers. The production method comprises thermal decoupling by means of thermistors that are free-standing or disposed on an insulation layer.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention is concerned with a layer sequence of asemiconductor component, a passive semiconductor component and a methodfor manufacture.

[0003] 2. Description of the Related Art

[0004] The invention is concerned with a thermistor as a semiconductorcomponent, for example, in bolometers. Polysilicon layers areconventionally employed as thermistors. Therein the temperaturesensitivity of the resistance, the so-called TCR-value, can be adjustedover a range by doping of the polysilicon.

[0005] From U.S. Pat. No. 5,260,225 a process is known for producing anintegrated, infrared sensitive bolometer employing doped polysiliconwith a TCR-value of between 1-2%/° C. The doping material is selectedfrom arsenic, phosphorous and boron. The IR sensitive polysilicon layeris provided on a thermally insulated silicon oxide layer, which servesto inhibit temperature transmission to the substrate.

[0006] Likewise, a device useful as a bolometer array is known from EP 0354 369, which is coupled to an integrated circuit with a boron dopedamorphous SiH resistor.

[0007] From U.S. Pat. No. 5,440,174 the use of WSiN-layers as resistorsand diffusion barriers in integrated circuits is known. By adjusting thenitrogen content of these layers it is possible to adjust both theresistance value as well as the diffusion inhibiting effect with regardto oxygen in a targeted manner.

[0008] Likewise the use of WSiN-layers in MESFETs are know fromTabatabaie, K (1995); IEEE Transactions on Electron Devices, Vol. 42,No. 7, pp. 1205. The preferred use of these layers is likewise concernedwith the diffusion inhibiting effect in combination with temperingprocessing during the production of GaAs-components.

[0009] No publications have until now disclosed in WSiN-layers thethermal characteristics depending upon the chemical composition of thelayers, and in particular, with regard to the relationship between theTCR-value and nitrogen content.

SUMMARY OF THE INVENTION

[0010] The invention is concerned with the task of providing a layersequence or structure and a therewith associated passive semiconductorcomponent with high TCR and low 1/f-noise, which can be produced inintegrated semiconductor construction techniques.

[0011] The invention with regard to the layer sequence is set forth inthe characterizing portion of Patent claim 1, with regard to the passivesemiconductor component is set forth in the characteristics of claims 4and 5, and with regard to the process for manufacture is set forth inthe characteristic portion of Patent claim 13. The remaining claimsconcern advantageous embodiments and further developments of theinvention.

[0012] The invention concerns a layer sequence of a thin layer resistorwith high temperature coefficient on a substrate. It is comprised offirst passivating layer, a WSiN-layer responsible for the temperaturedependent electrical resistance, and a first metalizing layer.

[0013] Preferably, between the first passivating layer and theWSiN-layer, there is an intermediate layer for thermal insulation. Theintermediate sequence layer is comprised of a polymide or BCB-layer(benzocyclobutene), which may be separately etched on substrates orbonding layers.

[0014] As the WSiN-layer material, in connection with the presentinvention, a substantially amorphous material is described, which in itschemical composition has a variable elemental content W_(X)Si_(Y)N_(Z)with x, y as main components and with incorporation of a smallproportion of z. With this WSIN a material, which has until now not beenused for this purpose, is employed, which exhibits a remarkably low1/f-noise also at higher TCRs, for example greater than 1%/° C. Besidesthis, the WSiN exhibits an absorption in the infrared radiation range,whereby a preferred use is in bolometers. Besides this, this materialcan be removed or etched from almost all substrate materials by a lowtemperature process.

[0015] The passive semiconductor component, structured in a layersequence, is comprised of a WSiN-residual layer which is employed as thethermistor of the inventive layer sequence. Between the electricalconnections there is an opening for passage-through of theelectromagnetic radiation to the thermal sensitive WSiN-Rest layer.

[0016] Below this opening there is also to be provided a second,radiation transmissive, passivating layer.

[0017] For thermal insulation, an intermediate layer sequence ispreferably provided between the substrate and WSiN-layer, which preventsa conductance of heat into the substrate. This intermediate layersequence for thermal insulation is only provided locally in the area ofthe radiation effect. The substrate itself can be comprised of amaterial with low thermal conductivity, for example, glass. In theemployment of silicon, preferably insulation layers of greater thicknessare employed and the silicon is separated or spaced apart below thethermistor.

[0018] For an application in the infrared range, the second passivatinglayer is correspondingly adapted for transmissivity for this type ofelectromagnetic radiation.

[0019] Besides the employment of intermediate layer sequences asinsulation layers, thermal insulation is preferably achieved in the areaof the opening for the passage-through of irradiation in the manner thatthe substrate, from the bottom side to the first passivating layer, iselectrochemically etched or removed.

[0020] A thermal decoupling of the substrate occurs either by etchingthe carrier material or by use of a layer with low thermal conductivity.

[0021] The process for producing a passive semiconductor component iscomprised in a sequence of process steps:

[0022] a first passivating layer is deposited on a substrate,

[0023] on the first passivating layer a WSiN-layer and a first metallayer are deposited over the entire surface,

[0024] the first metal layer is structured into a first connectionmetallization (metallization),

[0025] the area between the first connection metallization is coveredand the WSiN-layer is structured to a WSiN-residual layer as necessaryfor the construction component,

[0026] a second passivating layer is deposited and openings forelectrical connections are formed, preferably on the ends of theWSiN-residual layer,

[0027] in these openings metal contacts are introduced,

[0028] the part of the second passivating layer provided between themetal contacts is so designed or equipped, that an opening transmissivefor electromagnetic rays results.

[0029] A particular advantage of the WSIN materials, which werepreviously not employed for these purposes, results from thecharacteristic, that even at higher TCRs, for example greater than 1%/°C., they have an extraordinarily low 1/f-noise.

[0030] A further advantage with this type of WSiN thermal resistorresults from the ability to chemically deposit on almost all substratematerials. Thereby this material makes possible a simple and economicalproduction of this type of construction component.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In the following the invention will be described in greaterdetail on the basis of preferred embodiments with reference to schematicrepresentations in the figures. There is shown:

[0032]FIG. 1a-h method of manufacture of a thermistor with a freestanding layer in the radiation area,

[0033]FIG. 2a-d method of manufacturing a thermistor with a BCB-layer asinsulation layer,

[0034]FIG. 3a-e method of manufacturing a thermistor with a polyimidemesastructure as insulation layer.

DETAILED DESCRIPTION OF THE INVENTION

[0035] In one illustrative embodiment according to the FIG. 1 theprocess for manufacturing a thermistor with passive semiconductorconstruction element is described in detail. The process is comprised ofthe following process steps:

[0036] On a silicon substrate 1 approximately 400 μm thick, anapproximately 2 μm thick oxide layer is deposited as first passivatinglayer 2, preferably via a CVD-process (Chemical Vapor Deposition). Uponthis first passivating layer 2 a WSiN-layer 3 is deposited using thePVD-method (Physical Vapor Deposition) under defined addition ofnitrogen gas during the deposition process. Depending upon the nitrogencontent in the process gas the TCR-value and the mechanical layercharacteristics can be intentionally influenced over a broad range.Using the same PVD-method a WTi/Al-layer as first metal layer 4 (FIG.1a) is deposited or precipitated over the entire surface as cover layer.

[0037] In a further process the first metal layer 4 is structured into afirst connection metallization, in that with a first mask 5 the areasnot to be etched are covered, and by means of a wet chemical process thefirst metal layer 4 is eroded with the exception of the remainingresidual as first connection metallization 4′ (FIG. 1b).

[0038] The WSiN-layer 3 exposed to the surface following the etchingprocess is then, in the area between the first connection metallization4′, covered by a further second mask 6. The WSiN is removed in thesurrounding areas by RIE (Reactive Ion Etching). The WSiN-layerremaining under the mask 5 and 6 defines the active zone of thethermistor (FIG. 1c).

[0039] A further oxide layer as second passivating layer 7 is depositedwith an approximate thickness of 400 nm. In the areas of the firstconnection metallization 4′ openings for electrical connections arestructured at the ends of the WSiN-residual layer 3′ (FIG. 1d).

[0040] Metal contacts 8 of WTi/Au are introduced in these openings. Thepart of the second passivating layer 7 positioned between the metalcontacts is so designed, that this represents an opening transmissivefor electromagnetic radiation. In certain cases the passivating layer isthinned in the radiated area (FIG. 1e).

[0041] In further course of the process, for thermal decoupling, thesubstrate 1 is removed from the substrate bottom side up to the bottomside of the first passivating layer 2 in the area between the connectionmetallization 4′. For this the upper side is covered over with a thirdmask 9 (FIG. 1f).

[0042] With a fourth mask 10, of which the thickness is approximately 15to 20 μm, the substrate back side is covered and in the areas of theactive thermistor layer on the front side is opened for an etchingprocess. Due to the relatively thick substrate 1 a high rate etchingprocess is used for removing the substrate with the exception of thesubstrate residue 1′ (FIG. 1g). The construction component with afreestanding active thermistor layer produced by this process isrepresented in FIG. 1h.

[0043] Alternatively, between the WSiN-residue layer 3′ and the firstconnection metallization 4′, an intermediate layer sequence 13, 14 or asthe case may be 15 is etched and so structured that this providesthermal insulation to the substrate 1 (FIG. 1a). The intermediate layersequence is comprised of a carrier layer 13 and a BCB-layer 14 or, asthe case may be, a polyimide dummy layer 15 (FIG. 2d or as the case maybe FIG. 3e). In this case the substrate 1 is not etched for thermaldecoupling. The remaining process steps (FIG. 2b, 2 c; 3 b and 3 c)correspond essentially to the above described process steps.

[0044] In the case of the method represented in FIG. 2d the thermaldecoupling of the substrate is due to the thickness of the BCB-layer.For reducing the thermal resistance, the layers following upon theBCB-layer 14 are etched back laterally on the surface of the activethermistor (thickness of the BCB-layer corresponds to approximately25-75 μm).

[0045] In the case of the method shown in FIG. 3, for example, onepolyimide layer formed in an earlier stage of production is providedlaterally upon the later-formed thermistor structure (FIG. 3a) and thethermistor is thereafter produced (FIG. 3e) upon this mesostructureanalogously to the already described process steps according to FIG. 3b,3 c and 3 d. Finally the polyimide layer 15 is removed in an oxygenplasma process by means of an isotropic etching process. The empty space20 resulting below the thermistor results in a thermal decoupling withrespect to the substrate.

What is claimed is:
 1. A layer sequence for a thin film resistor withhigh thermal coefficient on a substrate, comprising: a first passivatinglayer (2), a WSiN-layer (3), and a first metal layer (4).
 2. A layersequence according to claim 1, thereby characterized, that between thefirst passivating layer (2) and the WSiN-layer (3) an intermediate layersequence (13, 14, 15) is provided for thermal insulation.
 3. A layersequence according to claim 2, thereby characterized, that theintermediate layer sequence includes a BCB-layer (15).
 4. A passivesemiconductor component, comprising: a substrate (1), a firstpassivating layer (2), a WSiN-residue layer (3′), a first connectionmetallization (4′), a second passivating layer (7) with openings forelectrical connection at both ends of the resistor layer, metal contacts(8) at the sites of the openings provided in the second oxide layer, afurther electromagnetic radiation transmissive opening provided betweenthe metal contacts (8) for radiation of the WSiN-residue layer (3′). 5.A passive semiconductor component, comprising: a substrate (1), a firstpassivating layer (2), a WSiN-residue layer (3′), an intermediate layersequence (13, 14, 15) for thermal insulation, a first connectionmetallization (4′), a second passivating layer (7) with openings forelectrical connection at both ends of the WSiN-residue layer (3′), metalcontacts (8) at the sites of the openings provided between the two oxidelayers, a further electromagnetic radiation transmissive openingprovided between the metal contacts (8) for radiation of theWSiN-residue layer (3′).
 6. A passive semiconductor component accordingto claim 5, thereby characterized, that the intermediate layer sequence(13, 14, 15) for thermal insulation is provided locally in the areaaffected by radiation.
 7. A passive semiconductor component according toclaim 6, thereby characterized, that the intermediate layer sequence(13, 14, 15) for thermal insulation includes a polyimide layer (15),which is removed by means of an oxide plasma, whereby at this area athermal insulating void (20) results.
 8. A passive semiconductorcomponent according to one of the preceding claims 4 through 7, therebycharacterized, that the substrate (1) is comprised of silicon or glass.9. A passive semiconductor component according to one of claims 1through 8, thereby characterized, that the first passivating layer (2)is an oxide layer with a thickness of approximately 2 μm.
 10. A passivesemiconductor component according to one of claims 1 through 9, therebycharacterized, that the opening transmissive for electromagneticradiation, for radiation of the WSiN-residue layer (3′), is covered overwith a second passivating layer (7), which is transmissive for infraredradiation.
 11. A passive semiconductor component according to one ofclaims 1 through 10, thereby characterized, that in the area of theopening the substrate (1) is removed up to the first passivating layer(2), for thermal decoupling.
 12. Use of a passive semiconductorcomponent according to one of the preceding claims, therebycharacterized, that the semiconductor component is employed asthermistor in a bolometer.
 13. A process for producing a passivesemiconductor component, comprising, depositing a first passivatinglayer (2) on a substrate (1), depositing a WSiN-layer (3) and a firstmetal layer (4) over the entire surface on the first passivating layer(2), structuring the first metal layer (4) using a first mask (5) into afirst connection metallization (4′), covering the area between the firstconnection metallization (4′) by means of a second mask (6) andstructuring the WSiN-layer (3) to a WSiN-residue layer (3′) necessaryfor the construction component, depositing a second passivating layer(7), in which openings for electrical connections are structuredoptionally at the ends of the WSiN-residue layer (3′) as resistancelayer, introducing metal contacts (8) in these openings, structuring thepart of the second passivating layer (7) provided between the metalcontact (8) such that this includes an opening transmissive forelectromagnetic radiation.
 14. A process according to claim 13, therebycharacterized, that the substrate (1) is etched or removed in the areabetween the connection metallization (4′) for thermal decoupling of thesubstrate bottom side up to the lower side of the first passivatinglayer (2).
 15. A process according to claim 13, thereby characterized,that between the WSiN-residue layer (3′) and the first connectionalmetallization (4′) a intermediate layer sequence (13, 14, 15) isdeposited and so structured, that this provides a thermal insulationwith respect to the substrate.
 16. A process according to claim 15,thereby characterized, that the intermediate layer sequence is comprisedof a contact layer (13) and a BCB-layer (14) or a polyimide layer (15),structured in such a manner, that this provides insulation in the areaof the thermal input towards the substrate (1).